The present invention concerns gear assemblies in general and, in particular, a method and apparatus for checking vehicle differential gear assemblies during manufacture.
In order to ensure the quality of completed differential gear assemblies, it is desirable to test such assemblies for various characteristics prior to shipping to the customer. For example, when the pinion nut is driven by a source of rotational power, and a braking force is applied to the differential carrier at the point where one of the axle shafts is normally coupled, the differential gear assembly should lock up. When the brake load is released, and the pinion nut continues to be rotated, the teeth on the gears in the differential gear assembly can be counted to calculate the gear ratio. When driven at low torque, the bearing preload and backlash can be measured. However, prior to the present invention, these characteristics were either checked individually or not tested at all during the manufacturing process.
For example, there is known a method and a apparatus for determining bearing preload in a gear train. An angular accelerometer is connected to a gear train so as to measure the deceleration of one of two meshed gears having backlash as the gears move independently of each other during the period after rotational power input to the gear train is disconnected when the backlash is taken up. The only resisting torque exerted on the one gear during the backlash takeup period is the drag torque of the preloaded bearing rotatably supporting it which varies directly with the bearing preload. The drag torque is determined from the measured deceleration and the bearing preload is determined from the drag torque. The gear having the faster inherent deceleration is connected to receive input power and drives the gear having the slower inherent deceleration. The input power is then disconnected to allow the faster decelerating gear to take up the backlash relative to the slower decelerating gear, and the deceleration of one of the gears is measured as the gears rotate out of contact with each other during the momentary period that the backlash is taken up. The drag torque and bearing preload of the bearings supporting the one gear are then determined from the measured deceleration.
In a conventional vehicle differential carrier assembly, a ring gear connected to the differential carrier assembly is driven by a pinion gear that is clutched to a source of rotational input power. To measure the deceleration of the differential carrier after the rotational input power has been connected and then disconnected, the input shaft of an angular accelerometer is extended through one axle shaft opening in the differential housing and is drivingly connected to the differential carrier in an area which is normally later occupied by one of the axle shafts. The pinion has a greater inherent deceleration than the carrier assembly due to the difference in the drag torques respectively exerted thereon and also the difference in rotational inertias. The difference in decelerations induces the gears to be free of each other during the momentary period after power removal so that the backlash between the gears is taken up, and the angular accelerometer measures the deceleration of the carrier assembly during this momentary period. The preload on the side bearings is determined from the measured deceleration, knowing that the only torque resisting rotation of the carrier assembly during the backlash takeup period is the drag torque exerted by the side bearings and knowing that the drag torque of the bearings varies directly with the bearing preload.
Another prior art apparatus for the dynamic testing of a pair of meshing gear wheels carries each of the gear wheels on a separate rotary support comprising pairs of aligned rotary spindles and having means for clamping the wheel under test between facing ends thereof. One spindle of each pair is axially displaceable to effect such clamping and the other spindle of each pair is connected to a rotary machine which can function both as a motor and a brake. Accelerometer transducers are mounted on one of the spindles of each pair to rotate therewith and thus with the wheels under test, the output signals from the transducers being fed via slip rings to processing circuits including means for summing and squaring them before passing the processed signals for display. The final signal is in the form of the accelerations or vibrations in a plane perpendicular to the axis of rotation of the wheel which are present as a result of tooth defects.
Another prior art process and apparatus for the quality control inspection of vehicle driving axles measures the acceleration transmitted from a vehicle driving axle comprising a differential unit and two half shafts to a support structure as the axle is driven against a resisting torque. Transmitted acceleration is measured in terms of its three-mutually-orthogonal components using accelerometers which output electrical signals to a processing unit. The unit processes these signals to derive comparison parameters which are then compared with reference values, to identify certain faults which may be present in components of the differential unit. The anomalies detectable by the inspection process include localized defects in the teeth of the driving and driven gears which cause cyclic discontinuous transmission of drive and "jolts", eccentricity of mounting of the driving and driven gears which causes a cyclic variation in the surface of contact between the teeth of the gears, irregular engagement between the teeth of the driving and driven gears, and operational defects of the bearings supporting the two gears.
A prior art automatic testing apparatus tests the circular spacing of gears, the deviations in gear concentricity, tooth thickness and tooth gap. The testing of circular spacing is accomplished in only one revolution simultaneously for both the right and left tooth flanks of the gear, and the measurement values thus obtained can be used as well for ascertaining the deviations in gear concentricity, tooth thickness and tooth gaps. During the testing operation, the gear is caused to rotate continuously in one direction from its own power source, and a slide on the frame of the apparatus is displaceable by a drive mechanism substantially radially toward the gear and back away from it for performing the individual testing operations. The slide has two measuring feelers supported pivotally on it, which are movable along with the gear counter to spring force and which cooperate with the preferably inductive transducer. The measuring feelers each point toward the same flank of two adjacent teeth in the vicinity of the pitch circle of the gear. Means are provided for applying the measuring feelers, under spring force, to the tooth flanks after the feelers have been driven into the tooth gaps and for moving them away from the tooth flanks, counter to spring force, after the testing operation. The first measuring feeler is embodied as a reference feeler and is connected with switching means by which, at a predetermined pivoted position of the feeler, the pickup or emission of a measurement value from the second feeler is brought about on the one hand and by which on the other hand the retraction of the measuring feelers out of the teeth and their re-insertion, retarded in an adjustable manner, into the teeth are controllable by means of the appropriate switching of the slide drive. A third measuring feeler which cooperates with a preferably inductive transducer is disposed on the slide in the vicinity of the pitch circle of the gear, being positioned for that purpose for the edge opposite the first or second measuring feeler. Thus, it is possible to scan the tooth flank opposite the first or second feeler, and to evaluate the measurement value thus ascertained for the purpose of ascertaining the spacing of the tooth flanks located opposite the first and second measuring feelers.